You can't place a portal on a moving surface in either game, so neither.

This was answered decades ago

According to a gravitationally accurate simulation a guy did for Youtube, the correct answer is_

... ah, ragebait answers only. Well, mission accomplished, probably >:3

Option B. Portals already break a couple of laws of physics and can reverse entropy, but I like to think you should look at the speed of an object relative to the portal.

Portals don’t stay on moving platforms.

But if they did, it would be A as the cube itself has no momentum.

Niether. Moving surfaces break portals instantaneously.

Ragebait answers only

I'm giving so many people Fs on this assignment because you failed to read all the instructions.

The correct answer is B due to the graphical conservation of speed lines.

If the downward moving portal hits the platform and there is some elastic rebound, then the object will bounce outward slightly.

Rage bait answer: Portals can't exist, it is from a child's game.

B.

Momentum/velocity is not an intrinsic property of an object, it is a relative property between two objects in a frame of reference.

Behind the yellow portal is the part of the universe where the blue portal is. The yellow portal, and therefore the space where the blue portal is, has momentum relative to the cube.

Put yourself in the frame of reference of the cube. You see the yellow portal come toward you. Imagine there are objects on the other side of that portal. You see those objects rush toward you through the portal. Why would the objects just stop dead when you came through the portal? (If they did just stop, it would be as though you hit a wall, and you wouldn't actually go through the portal at all.)

"speedy thing goes in, speedy thing comes out."

So stationary thing goes in, stationary thing comes out.

The object going into the portal has no momentum so it would be A.

Momentum is conserved when passing through a portal. In the reference frame of the out portal, the object has no momentum, so it plops out.

Speedy thing goes in, speedy thing comes out.

Cube had no speed going in, therefore no speed going out. The portal speed is irrelevant

Portals aren't real and so work however you want them to, but people rarely consistently apply their models.

I'd say A given how they work in the games though. Only the object's momentum is conserved. The portal doesn't transfer momentum. There may be a slight breeze coming out of the blue end as the column of air in front of the portal-plate is pushed in, but the cube is just going to flop out.

I choose A because that would mean I could use the portal to fuck myself in the ass easier.

If we're only supposed to do ragebait answers, then anyone who passed 3rd grade science would be able to tell you the answer is obviously B

If you actually played the game, and paid attention in physics class in highschool, then you would know the answer is clearly A, and everyone who says it is B really needed the simplified explanation from GLaDOS to understand how to play the game.

It went through the portal at speed, so it should exit the portal at speed. That’s my take.

https://www.youtube.com/watch?v=B19nlhbA7-E

Not providing a link to alternative platforms is my ragebait

The question is: Is it the velocity of the object relative to the portal that matters or the velocity of the object in some other frame of reference?

In the later case, we must ask how the portals at different angles don’t send objects flying off at the speed of the milkyway’s travel through the universe.

The answer that requires the least assumptions and justifications is B.

Since nobody seemingly posted link to this absolute ... Idk, gold? It's about actually simulating space(-time?) with portals: https://youtube.com/@optozorax_en I see offspec's comment is mentioning the guy, yeah. Tldr answer is complicated.

...

Ah, ragebait answers only. Ugh, worm! Arrrr! I am so angry roar grrrr.

Both portals stationary: object velocity unchanged.

Both portals moving at the same speed: object velocity unchanged.

Entry portal moving: object pushed out at the same speed it entered.

Exit portal moving faster than object entered: object explodes.

My take:

The cube's mass is x (eg one gram) and its velocity is zero, therefore its momentum (m*v) is zero. Objects in motion tend to stay in motion, while objects at rest (e.g. momentum of zero), tend to stay at rest.

The thing which is moving, is the portal. At best, the event horizon of it reaches the leading-end then the trailing-end of the cube at the speed the portal is moving over the depth of the cube. If the portal moves faster, that distance is covered faster, and the full cube is entirely on the other end of the other portal faster [than a slower moving portal].

Since going through the portal is a frictionless and forceless action, the speed at which the portal fully envelops the cube would neither add nor remove momentum upon it. And if the cube did have its own momentum it would be maintained, but since it does not, the cube would not move until another force, like gravity, acted upon it.

So, A.

Neither, I've already gleefully incinerated that fucking cube before it got to this point.

a. while the portal travels down it collects air, increasing air pressure on the other side, meaning once it reaches the cube, the increased air pressure has mad the air solid so the cube cant fly through it.

Neither. The cube is not making contact with the portal at all, since the portal is on a stationary block with some speedy lines drawn on it. Speedy lines don't nake thingy go fast - everyone witb a gel-hairstyle knows that.

The answer is definitely B (see other comments), but I think the more interesting question is, how does it affect the portals themselves and the surfaces they're attached to?

When the portals are attached to a solid unmovable wall (as in the games), we can pretty much ignore the forces acting upon the wall as they will just be automatically cancelled out by the normal force. But the same does not apply for portals attached to detached panels. Let's say that instead of a piston pushing down, the portal is attached a free-falling panel with the portal facing down.

We are inclined to assume that as the portal falls onto the cube, it feels no force, as if it fell through air or through a vacuum. But is that really the case? Maybe instead, the falling portal experiences resistance from the cube? Or even, actually, an accelerating force?

Let's assume conservation of momentum at each end of the portal. That is, in the general case: if the portal (which we assume has no mass) is attached to an object with mass M and velocity V, and "swallows" a cube or other object with mass m and velocity v, and at the end of this interaction the portal-surface object with mass M has velocity V', then we expect:

M × V' = (M × V) + (m × v)

Mass is not conserved because the cube was transferred to the other portal.

Solve for V':

V' = V + (m/M) v

This is a strange result. The cube's momentum is imparted into the portal, but the result would be different depending on our reference frame. From a reference frame tracking the cube pre-interaction, v = 0 (by definition) and so V' = V, the portal-surface object has no change in velocity. But in any other reference frame, it does.

Physics can't be affected by reference frame (thanks, relativity) so this analysis must be wrong.

... I'll keep thinking on this.

A, momentum is in the portal, not the cube

The "ragebait answers only" in the OP is the only thing stopping me from actually raging at everyone saying A. I am giving them all the benefit of the doubt, they're deliberately saying the wrong answer.

Everyone saying B missed the assignment and answered accurately.